This invention pertains to a process of making lignocellulosic pulp. It pertains particularly to a process of making lignocellulosic pulp in high yield at low cost by first mechanically defiberizing lignocellulose in an atmosphere of steam and thereafter digesting the pulp in the presence of lime.
The conversion of lignocellulose to fibrous pulps is a sophisticated art which supplies to industry on the large commercial scale pulp products ranging from the mechanically produced pulps through the semi-chemical pulps, to the highly refined, bleached full-chemical pulps, which preserve fiber length to a high degree. Need nevertheless exists for a process which will convert lignocellulose rapidly and easily, at low cost, to high yields of a fibrous pulp having a degree of refinement greater than that possessed by mechanically produced groundwood, and accordingly applicable to uses not requiring long fiber length, but to which the mechanically produced pulps are not adaptable.
Such an application exists, for example, in the manufacture of hydrated cellulosic gels. These gels have important uses, including applications as adhesives. They currently are produced by mechanically refining cellulose fibers in aqueous medium under conditions such that the cellulose takes on water of hydration in varying degree and is converted to a gel. Purely mechanical pulps which may be produced in high yield are not suitable for this conversion. Accordingly, full chemical pulps which are obtainable from lignocellulose in yields of only about 46% by weight are employed as raw materials for cellulosic gel making.
It obviously would be an advantage, and it is an object of this invention, to provide a process for converting lignocellulose to a cellulosic pulp suitable for use in the manufacture of hydrated cellulosic gels, the pulp being produced in high yields of the order of 85% or more, based on the dry weight of the lignocellulose employed in their manufacture. Obtaining the pulp products in yields of this order of magnitude obviously results in a highly significant saving in pulp cost. It also results in a highly significant conservation of the timber resource.
Still other objects of the present invention are the provision of a process for making cellulosic pulps in high yield and at low cost which is applicable to a wide range of lignocellulosic starting materials; which is easily and rapidly carried out in simply relatively low cost equipment; which requires but a single low cost pulping chemical, available universally in unlimited quantities; and which is characterized by relatively moderate power requirements as well as by minimum problems of waste disposal, since minimum effluent is produced.